Can't use DrillSideways with both RangeFacetRequest and non-RangeFacetRequest

Details

Description

I tried to combine these two and there were several issues:

It's ... really tricky to manage the two different
FacetAccumulators across that N FacetCollectors that DrillSideways
creates ... to fix this I added a new MultiFacetsAccumulator that
switches for you.

There was still one place in DS/DDQ that wasn't properly handling
a non-Term drill-down.

There was a bug in the "collector method" for DrillSideways
whereby if a given segment had no hits, it was skipped, which is
incorrect because it must still be visited to tally up the
sideways counts.

Separately I noticed that DrillSideways was doing too much work:
it would count up drill-down counts and drill-sideways counts
against the same dim (but then discard the drill-down counts in
the end).